Rangemaster build / behavior question

[kosmonautmayhem]

Hi all,

I just put an NPN Rangemaster clone together. It sounds great, but I'm having issues with the boost knob maxed when I hit the strings hard. It sort of farts out if I hit my low E and A string hard. Playing medium to light, it doesn't act up.

----some background info and my setup-----

Bias on the collector is +7.14v

Pedal is stock except I've added a switch to choose between two input caps (.068uF / .022uF). My output cap is .022uF.
(After socketing them these were the values that worked best with my Fender amps)

My tests haven't been at full volume yet, since I've not had a chance to take it out and crank it. I'm running guitar (tele, les paul or jazzmaster - all passive pickups) > Rangemaster (cranked) > Barber LTD > MXR Dyna Comp > Boss Tu-2 > Amp (Princeton Reverb or Princeton 6G2 - volume about 3 or 4)
-------------------------------------------

Is my problem an impedance mismatch between other effects or guitars and the RM? Is this what I can expect since the RM at full tilt is pushing lots of dBs?

Can't figure this out. Perhaps I should bias the transistor cooler? The only way I can minimize the effect is to lower the boost knob to about 2 o'clock, or roll back my guitar volume, but then I lose a lot of dirt, which is no fun!


Cheers!
kM

[mojah63]

Normally it's biased at 4.5v and the sweet spot for the volume is between 12 and 2 oclock.

[kosmonautmayhem]

Thanks Mojah! I'm not too experienced with RMs. The Fuzz Face style builds I've done have all been biased about +/-4.5v. So its typically the same for Rangemasters as well???

I'm glad my issue sounds like a mis-bias'd transistor.

Thanks for the tip on the 'sweet spot'!

[mojah63]

You're welcome. There's a page about rangemasters at geofx. I put a rotary switch on mine with 8 different input cap values. That and a grey dod 250 clone are my only dirt boxes on my board. You used a germ transistor? Its like a fuzz in that it likes to be first seeing the guitar as a input load.

[kosmonautmayhem]

Thanks. I'll give that another read. I poured over the RM article but it was some time ago. I thought there was something in there about biasing at 7v, but I could be totally wrong. Yes, I love the character this pedal has, its great! I want to build a few more with tweaked input cap values...a rotary switch sounds very nice! :) I'm currently using a DPDT to toggle .o68uF and .022uF on the input and love the sounds I'm getting - just not when its farting out!

I'll try to cool down the bias and see where that gets me. And yes, its first in line, followed by a Barber LTD.

Cheers

[Keyser Soze]

Yeah, offhand it sounds like your bias is a bit off and the farting is simply the signal bumping up against the supply rail, try lowering the bias and seeing if that solves the problem.

[kosmonautmayhem]

Today I added a 10k bias trimpot and dialed it in around 4.5v. This cleaned things up nicely andthe pedal still has the classic sound - although now its not quite as muddy as before! :)

I was still getting the troublesome farting lows, but I discovered this is only when running before my Barber LTD. As long as I back off the 10kA volume/boost knob on the RM I'm golden. It only happens in the last 20% of its taper, btw.

Perhaps there's an impedance issue or something or maybe the Barber is gating the RM since its volume was set lower than the RM???

Thanks so much for the advice guys!

kM

Now to build some more of these... :)